Each of the four monkeys received two capsules of NORPLANT containing 70 mg of Levonorgestrel (LNG) in silastic rods. The capsules were inserted subdermally in a "V" pattern to the inter-scapular area. Blood samples were obtained once prior to treatment, daily from days 1 through 7, once per week to day 896, then biweekly to the present (day 1258). All sera was analyzed for LNG content by radio-immunoassay. Initially, the implantation site was observed for any localized reaction to the capsules, then palpated periodically to check for any migration or diminishing size of the capsules. In addition, animals' menstrual calendars were monitored for any changes in frequency, absence and duration of cycle length. During the previous year, capsules were no longer palpable, so this procedure was not performed during this year. During this year the animals' menstrual calendars have shown amenorrhea for one of the four animals and a single light bleeding episode for the other three animals. Serum analyzed for LNG showed levels remaining fairly constant at 2.02 ng/ml (SEM 0.3) on day 875 to 2.37 ng/ml (SEM 0.2) on day 1050. LNG levels then started to drop slightly from 1.87 ng/ml (SEM 0.2) on day 1064 to 1.45 ng/ml (SEM 0.1) on day 1258. One of the four animals assigned to the study, died after day 1050 of the study from peritonitis and pleuritis. The other three remaining animals will continue to be monitored on a biweekly schedule until serum LNG drops below contraceptive effectiveness, which is 0.3 ng/ml. *KEY*Levonorgestrel, NORPLANT(, Steroidal contraception, Subdermal implants, Synthetic progestin